Process for the treatment of wood



United States Patent Ofifice 3,085,039 Patented Apr. 9, 1963 3,085,039PROCESS FOR THE TREATMENT OF WOOD Wilhelm Giirtner, Neunkirchen,Germany, assignor, by mesne assignments, to FMC Corporation, New York,N.Y., a corporation of Delaware N Drawing. Filed Aug. 23, 1960, Ser. No.51,273 4 Claims. (Cl. 162-78) This invention relates to thedecortication and peeling of wood, by a process which renders the Woodparticularly receptive to subsequent treatments in the production offibrous products.

In the preparation of fibrous materials from vegetable raw materials, itis becoming increasingly important to provide a high degree of whitenessand purity in the fibers. Mechanical and chemical purification andbleaching processes for such fibrous materials have been highlydeveloped, with processing frequently being carried out in severalstages. Normally, the wood is decorticated or washed before it issubdivided mechanically or chemically into fibers, and the bleachingprocess is carried out as a distinct step thereafter.

Previous decortication methods have not been satisfactory, and havereduced the efficiency of subsequent treatments. Contaminants notremoved in the decortication follow through to finished products, whichinclude fine writing papers. In some cases, the contaminants make itimpossible to upgrade the fibers, and at best they make necessary agreater expenditure of chemicals for bleaching and other purificationtreatments.

For these and other reasons, it is important to remove as many of thenatural impurities as possible from the fibers before they are bleached.However, it has been found in practice that this cannot be achievedwithout undue losses in fiber substance, or in other reduction ofquality, for example, in the decolorizing of the fibers which occurswhen they are pretreated with steam. Removal of steaming-induced browncolorants, or of best and bark particles carried over from the wood,causes great difficulties in the treatment and application of thefinished fibrous material. These contaminants often cannot be removed bythe chemicals used for later process ing, such as the peroxide used inbleaching.

The processing involved in decortication and peeling of wood also haspresented a problem. For example, it has been considered necessary totreat the wood for a long time in a decortication drum and subsequentlyto sort the product by hand to eliminate poor grade materials. It alsohas been considered necessary to cut off the dirty faces of roundtimbers, thus providing considerable wood losses and additional labor.

It has now been found that the above difficulties can be avoided ifwood, preferably undecorticated wood, is treated with aqueous solutionof active-oxygen compounds in an about neutral to acid medium, and undersuperatmospheric pressures at temperatures below about 60 C.

Active-oxygen compounds such as H 0 peracids, or their salts, forexample peracetic acid and perborates, are compounds which liberateoxygen and are useful in the process of the present invention. They areemployed as aqueous solutions in an amount to provide the amount ofactive-oxygen present in about l-40%, and preferably about 320% of 100%hydrogen peroxide.

In the process of the present invention, it is not necessary to subjectthe wood to a mechanical treatment before it is contacted with theactive-oxygen compound, as has hitherto been customary in thepreparation of fibers. The process is preferably carried out onundisintegrated wood. However, the treatment can also advantageously becarried out on disintegrated wood, and results in better cleaning of thewood and removal of bark from it.

The pressure applied in the present treatment advantageously will beabout 4-15 atmospheres gauge. The process is carried out at or aroundroom temperature, normally at about 20 C. to C. Under these conditions,a high concentration of chemicals can be ob tained in the wood.

Operation at an acid or neutral pH makes it possible to compress largeamounts of the present chemicals into the wood. When alkaline solutionsare used, this is not possible because of the alkali-induced swelling ofthe wood. When the present acid or neutral solutions are compressed intothe wood, a reaction begins within the wood whereby bark and bast, aswell as other impurities still adhering to the wood, are forced from thesurface of the wood.

Wood treated in this way can be freed from bark and hast indecortication tunnels much more easily than wood treated with steamaccording to known processes. A completely clean decortication isobtained even in branch positions, where rings of bark or bast oftenprovide difficulty. As one desirable result of the present treatment thehast, which is very strongly bound to the wood, is forced off fromwithin and hangs very loosely from the wood, so that it is very easilyremoved. When wood treated in this way is put into a decortication drum,it is possible to obtain complete decortication in a sub stantiallybriefer time than in the case of wood which for example has beenpretreated with steam at 96 C. for four hours. The faces of the woodpieces are likewise cleaned, so that they no longer must be cut off anddiscarded as is customary where dirty wood is treated considerablesaving in manpower and lessened wood loss.

The wood is advantageously impregnated with the present aqueoussolutions of active-oxygen compounds in a pressure tank, for example, atabout 4-15 atmospheres gauge pressure for about 2-4 hours. Followingthis, it may be directly introduced into a decoriication drum in whichit is tumbled, and loosened bark and bast are abraded from it.Surprisingly, practically no active-oxygen loss due to decompositionresults from this treatment, even with the application of a very highlyconcentrated peroxide. When alkaline solutions were used, for example incaustic bleaching processes, substantially larger losses result. Thisnew process accordingly differs from past processes in that theperoxidic compounds liberating oxygen are applied in about neutral orweakly acidic solutions, preferably at room temperature and at anelevated pressure.

Woods pretreated by the present method are surprisingly clean. They aremuch cleaner than steam-treated wood, which is brownish and notcompletely free of bast, and therefore they introduce substantially noimpurities into subsequent operations, such as bleaching. This meansthat the finished product is much cleaner and accordingly of greaterquality both in appearance and physically.

A further advantage of the present process is that as long as theactive-oxygen chemicals are present in the wood, a slow oxidation takesplace even in a neutral or acid medium. It is known that the amount ofoxygen liberation from these chemicals can be increased by raising thetemperature, or by adding alkalies. Oxidation within the fiber structurecan thus be accelerated at any desired time. Accordingly, due to thesuperior ability of the present neutral or acid solutions to penetratethe wood, chemical reactions can be caused to take place within timbersof substantially any thickness. These reactions have the surprisingadvantage that in addition to the expected bleaching which takes place,a marked disintegration of the fiber structure is provided. Accordingly,later disintegration is facilitated by the present treatment of the rawmaterial, and at the same time a Example 1 Five cubic meters of sprucewood was impregnated in a pressure tank made of refined steel with an 8%hydrogen peroxide solution at a pressure of 7 atmospheres gauge pressurefor 3 hours. After this treatment, the wood was decorticated andprocessed further in a decortication drum in a usual and known way. Theproduct was clean and free of bast and bark.

Example 2 Five cubic meters of poplar wood was treated in a pressuretank with a 6% peracetic solution at room temperature and a pressure of8 atmospheres gauge pressure for two hours. The wood was then freed ofbark and bast by means of drum decorticat ion, and was then 4 processedin a four-press grinder to form mechanical wood pulp. The pulp was ofhigh purity and free of bast and bark particles.

What is claimed is:

1. Process for the treatment of undecorticated wood, comprisingimpregnating the Wood with a neutral to acidic aqueous solution of aperoxy-containing activeoxygen compound at a pressure of about 4 to 15atmos pheres and at a temperature below about 60 C.

2. Process in accordance with claim 1, wherein the treatment takes placeat about room temperature.

3. Processes in accordance with claim 1, wherein an aqueous solution isemployed which contains the peroxy-eontaining active-oxygen compound inan amount of about 1 to 40%, calculated as hydrogen peroxide.

4. Process in accordance with claim 3, wherein the peroxy-containingactive-oxygen compound is present in an amount of about 3 to 20%,calculated as hydrogen peroxide.

MacMahon Sept. 26, 1944 Dreyfus Feb. 19, 1946

1. PROCESS FOR THE TREATMENT OF UNDECORTICATED WOOD, COMPRISINGIMPREGNATING THE WOOD WITH A NEUTRAL TO ACIDIC AQUEOUS SOLUTION OF APEROXY-CONTAINING ACTIVEOXYGEN COMPOUND AT A PRESSURE OF ABOUT 4 TO 15ATMOSPHERES AND AT A TEMPERATURE BELOW ABOUT 60*C.